NIOS SSC SCIENCE LESSON Chapter 27

7/31/2019 NIOS SSC SCIENCE LESSON Chapter 27

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Respiratory Gaseous Exchange and Elimination of Body Wastes : 205 :

27.1 NEED FOR RESPIRATORY GASEOUS EXCHANGE

Every cell of our body needs to produce energy for its activities. This energy is

produced by oxidising the food (glucose), which the cell receives as product ofdigestion. Oxygen is required for oxidation of glucose in the cell. The intake of

oxygen for the release of energy by its action on glucose is termed as respiration.

27.2 BREATHING AND RESPIRATION

The mechanism by which organisms obtain oxygen from the environment and

release carbon dioxide into it is termed breathing.

Respiration in ordinary sense is a wider term, it includes breathing as well as

(i) exchange of oxygen and carbondioxide in the tissues, and

(ii) action of oxygen on glucose inside the cell to release energy (oxidation).

27.3 RESPIRATION IN PLANTS

Plants do not have any special respiratory

organs. Roots take up oxygen by means of root

hair (Fig. 27.1). Root hair are embedded in the

soil. Oxygen in the air surrounding them

diffuses into the root hair and from there into

the roots. The carbon dioxide given out,

similarly, diffuses out through roots. You may

check the mechanism of diffusion in the lesson

26 on transportation.

Tiny apertures called stomata (Fig. 27.2)

are found on the surface of the leaf. They have

a mechanism for opening and closing. They

open to let in oxygen and release carbon dioxide.

In the older parts of roots or bark of woody

plants, tiny openings called lenticels

are present. It is through these

lenticels that oxygen reaches the

inner living tissues and carbon

dioxide moves out.

CHECK YOUR PROGRESS

27.1

1. Roots are present below the soil.

Do they pick up oxygen from air

surrounding the root hair or from the

water surrounding them?

2. Name the apertures found on the

green stems and leaves that let in

oxygen.Fig.27.2 Opening and closing of stomata

Closed Open

Turgid

guard cell Thick cell

wall

Thin cell

wall

Stoma

open

Flaccid

guard cell

When a plant has plenty of water,

the guard cells become turgid. The

cell wall on the inner surface is very

thick, so it cannot stretch as much

as the outer surface. So as the guard

cells swells up, they curve away

from each other, opening the stoma.

When a plant is short of water, the

guard cells become flaccid closing

the stoma.

Stoma

closed

Fig. 27.1 Root hairs

Lateral root

Primary root

Root hairs

Apical meristemRoot cap


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: 206 : Respiratory Gaseous Exchange and Elimination of Body Wastes

3. The bark of woody plants is dead but the inner layers inside the bark are

living. How do they get oxygen and release carbon dioxide?

4. Differentiate between breathing and respiration.5. How does respiration help in the release of energy?

27.4 RESPIRATION IN ANIMALS

Animals have special organs for respiration. Most aquatic animals have gills (e.g.

fish, prawn). The major organs for respiration in land animals are the lungs.

Fig. 27.3 Gill and lung breather

27.4.1 Respiration in human

beings

Like other land animals, human

beings take in oxygen from the

surrounding air and release carbon

dioxide into it.

27.4.1a Respiratory system

Respiratory system of human beings

has the following parts (Fig. 27.4).

External nares or nostrils

Nasal cavities inside the nose

Internal nostrils opening into

pharynx

Pharynx that leads into the wind

pipe or trachea

Trachea divides into two bronchi

(sing bronchus) which lead into

the two lungs Fig. 27.4 Respiratory system in human beings

BronchioleBranch of pulmonary artery

Branch of

pulmonary vein

Alveoli covered

with capillaries

Alveoli

Alveoli cut open

Voice box

Right lung

Bronchiole

Rib

Heart

Diaphargm

Ribs

Bronchus

Wind pipe

(a) Fish (gill breather)

(b) Human (lung breather)

Nostril

Tongue

Rib

Bronchiole

Diaphragm Heart

Bronchi

Left lung

Trachea (windpipe)


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The opening of the pharynx into the trachea is called glottis. Trachea is thin

walled but its walls do not collapse even when there is negligible amount of air in

it as it is supported by rings of cartilage.Lungs enclose within them branches of bronchi called bronchioles which

branch further and end in very thin walled sac-like structures called air sacs or

alveoli (sing. alveolus).

27.4.1b Mechanism of breathing or Ventilation of lungs

Lungs are located in the chest cavity or the thoracic cavity. Below the chest cavity

is the abdominal cavity. These two cavities are separated from each other by a

dome-shaped (upwardly arched) muscular sheet called diaphragm (see figure).

The movements of this diaphragm help in breathing. Breathing, also called

ventilation of the lungs involves two processes inhalation (taking the air inside)

exhalation (forcing the air out)

(i) Inhalation (drawing the air inwards) (Fig.

27.5a) is the result of increase in the volume

of the thoracic cavity. This increase is caused

by the changes that take place in the position

of diaphragm and ribs.

Diaphragm straightens out

Ribs are raised upward and outward and

volume of chest cavity increases.

The air drawn in brings in oxygen which

diffuses into the alveolar air.

(ii) Exhalation (Fig. 27.5b) is the result of

decrease in the volume of the thoracic cavity.

This decrease in the volume is caused due to

the following:

Diaphragm relaxes and resumes its dome-

shape arching upwards.

Ribs are lowered downward and inward.

The thoracic cavity is compressed and

the pressure inside the lungs is increased. Air

is pushed out through the trachea and nose.

The alveolar carbon dioxide diffuses out.

This breathing out of carbon dioxide laden

air is called exhalation.

You can breathe heavily and feel your

chest go up and down.

Fig. 27.5 How the thorax changes

shape during breathing

(a) Inhalation

(a) Exhalation

Diaphargm is

pulled down

Volume of thorax

increases, so air is drawn

into the lungs

Rib cage is raised

Trachea

Rib cage drops down

Volume of thorax decreases,

forcing air out of the lungsDiaphargm

springs up


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Breathing rate

When at rest, an adult human breathes about 16 to 18 times per minute.

Breathing rate increases during physical exercise, disease, fever, pain and

under stress.

Exchange of gases between blood and tissues

Inhalation fills in the alveoli of lungs with oxygenated air. This oxygen has

to reach the various tissues of the body. Thus as the first step, blood capillaries

on alveoli (Fig 27.6) pick up oxygen from alveoli and carbon dioxide brought

by the capillaries from the tissues is exchanged for oxygen and diffuses

into alveoli.

Fig. 27.6 Exchange of gases between blood and alveoli

In the tissues, oxygen gets used up and carbon dioxide is accumulated which

is now exchanged for oxygen. The carbon dioxide picked up by blood from tissues

is carried to the heart through veins.

27.4.1c Cellular respiration

Once inside the tissues, oxygen acts upon the digested food (glucose) which has

reached the cells of the tissues. As a result energy and carbon dioxide are released.

This occurs in the mitochondria of the cells and is called cellular respiration.

Respiration suffers at high altitudes and great depths. Do you know why

mountaineers and sea divers carry oxygen cylinders and wear oxygen masks?

As we climb higher and higher altitudes, the air pressure becomes lower and

lower. Reduced oxygen supply causes breathing troubles and oxygen masks

facilitate breathing. People living in hilly areas have evolved adaptation such as

increased number of red blood corpuseles and large thoracic cavity.

Divers carry oxygen masks because we derive our respiratory oxygen from

air and not water.

Bronchiole

Alveolus

Blood vessels return

oxygenated blood to

the pulmonary veins

Cell in wall of

capillary

Elastic fibreRed blood

cell

White blood cell, which can destroy

bacteria that get into the alveolus

Air space in

alveolus

Cell in wall

of alveolus

(a) Alveoli

Blood vessels bring

blood without

much oxygen from

the pulmonary

veins

(b) Section through part of a lung (magnified) (c) Gaseous exchange in an alveolus

CO2diffuse

out

O2

diffuse in

Layer of

moistureRed blood

cell

Wall of

alveolus

Air moves in and out

Wall ofcapillary


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27.4.1d Artificial respiration

A victim of an accident like drowning, electric shock or inhalation of poisonous

gas suffers from asphyxia or the condition of lack of oxygen. The symptomsare blueing of lips, fingernails, tongues and stoppage of breathing. In such cases

mouth-to-mouth respiration is given.

You must have realised how important respiration is for survival. Medical

technology has introduced certain gadgets like the oxygen mask and ventilators

which aid in respiration when a patient develops breathing problems. Often these

help the patient to overcome respiratory problems.

27.4.2 Respiratory disorders

Two common diseases of the respiratory system are bronchitis and pneumonia.

27.4.2a Bronchitis

In bronchitis, the bronchi and bronchioles get inflamed and their cavities become

narrow so that air cannot pass in and out of lungs easily. The pathway gets

constricted either due to accumulation of mucus on the walls of the bronchi or

bronchioles. This happens due to excessive smoking. Also infection of the

accumulated mucus leads to inflammation of walls of the lungs and bronchi,

which narrow the airways and cause difficulty in breathing.

27.4.2b Pneumonia

Pneumonia is caused by pneumococci bacteria. These bacteria attack the trachea

and bronchi and spread to the terminal bronchi. Symptoms of pneumonia areshivering, vomiting and continuous fever. Antibiotics have to be administered to

cure bronchitis and pneumonia.

CHECK YOUR PROGRESS 27.2

1. Why does the trachea not deflate (collapse) when the air is pushed out?

2. Name the parts of the human respiratory system in a sequence starting from

the nose.

3. State the events which occur during inhalation.

4. In which organelle of the cell does cellular respiration occur?

5. Why are the alveoli supplied with capillaries?

27.5 EXCRETION

Many chemical reactions take place inside the body cells. Some products of

these chemical reactions are not needed by the body. They may even be harmful.

Most of these waste products contain nitrogen and therefore they are termed

nitrogenous waste products. Their removal from the body is called excretion. We

shall now learn about the excretory organs and mechanism of excretion.

27.5.1 Excretion in plants

In plants, breakdown of substances is much slower than in animals. Hence

accumulation of waste is much slower and there are no special organs of excretion


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in plants. Carbon dioxide released during respiration gets utilized during

photosynthesis.

However, a number of chemical substances which are formed as byproductsduring certain activities of plants, are known to be thrown out of the plant and

deposited on the bark, old wood, old leaves etc. These substances may be

nitrogenous such as alkaloids, or non-nitrogenous such as oils, resins and crystals

of silica.

The alkaloids include Quinine, which deposits in the bark of the cinchona tree

and is a medicine for malaria; Morphine in poppy fruits was used as an anaesthetic.

Caffeine, which yields the beverage coffee is deposited in coffee leaves.

The non-nitrogenous substance exuded by plants include: tannins found in

tea leaves, essential oils such as are deposited in leaves of tulsi and lemon and

Eucalyptus, resins thrown out are deposited on the bark of pine trees. We useresins in varnish and polish. In certain grasses crystals of silica are deposited by

the plant.

27.5.2 Human excretory system

In human beings, excretion is carried out

by an organ system known as the urinary

system or the excretory system. See the

figure (Fig.27.7) and locate the following

parts:

Two bean shaped kidneys, locatedbelow the diaphragm in the abdomen

and towards the back.

Two excretory tubes or ureters, (one

from each kidney).

One urinary bladder, ureters open

into it.

A muscular tube called urethra arises

from the bladder. The urinary opening

is at the end of urethra.

27.5.2a Structural and functional unit

of the kidney Nephron

Each kidney is made of tube like structures called nephrons (renal tubules). A

nephron is the structural and functional unit of the kidney. The cup-shaped upper

end called Bowmans capsule, has a network of capillaries within it called

glomerulus. Glomerulus is a knot of capillaries formed from the artery which

brings blood containing wastes and excess of water to the kidney. Bowmans

capusle leads into a tubular structure.

The tubular part of the nephron or renal tubule has three sub-parts, the

proximal convoluted tubule (PCT), a thinner tube called loop of Henle and the

Fig.27.7 Human excretory system

Urethra tube (leading from bladder

out of body)

Sphincter muscle (when

relaxed urine can leave

body)

Blood vessels

Kidney

(makes urine)

Ureter (carries

urine to the

bladder)

Bladder

(stores urine)

Diaphragm


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distal convoluted tubule (DCT) (Fig. 27.8). Blood

capillaries surround these tubules.

27.5.2b Mechanism of excretion

Blood leading into the glomerulus gets filtered in

the Bowmans capsule and is called the nephric

filtrate. The red blood corpuscles and proteins do

not filter out.

The filtrate which now comes into the renal

tubule not only contains waste but also useful

substances. The useful substances get reabsorbed

from the tubule into the blood capillaries

surrounding the tubule. Excess water and salts like

sodium and chloride also get reabsorbed into the

blood from the renal tubule. Thus, the waste alone

which is primarily in the form of urea enters into

collecting tubules from various renal tubules. It is

the urine.

From the kidneys, the urine enters the ureters

to reach the urinary bladder where it is stored

temporarily. The urine is thrown out periodically

through the urinary opening.

27.5.2c Functions of the kidneys Excretion of nitrogenous wastes,

Regulating the water content of the body

(osmoregulation), and

Keeping the normal mineral balance in the blood. When this balance is upset,

a person can fall sick.

27.5.3 Other organs that remove waste from our body

Apart from kidneys, some other organs of the body also remove waste from the

body. These organs are as follows (Fig. 27.9)

Fig. 27.9 Some organs of our body that remove waste

Fig. 27.8 Structural and functional

unit of the kidney Nephron

Ureter

Renal vein

Renal artery

(b) One nephron (highly magnified)

(a) A KidneyUrine

Branch of

renal artery

Glomerulus

Bowmans capsule

Proximal convoluted

tubule

Capillaries

Branch of

renal vein

Loop of Henle

Collecting duct

Capillaries

Distal

convoluted

tubule

Cells

Blood

Excess

Heat

Urea

Excess

water and

mineralsCarbon dioxide

Oxygen

Lungs

LiverSkin

Kidney

Amino acids

Glucose

Heat


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Sweat glands in the skin remove excess salts when we perspire.

Lungs remove carbon dioxide.

Rectum (large intestine) removes undigested food.27.5.4 Maintenance of the internal environment

A person gets sick if the balance of substances such as mineral ions, water or

even hormones inside the body is upset. Maintenance of the correct amount of

water and mineral ions in the blood is termed osmoregulation. Osmoreulation is

a function of the kidney.

Homeostasis means maintaining a steady state inside the body. It requires the

regulation of all substances inside the body in the correct amount and proportion.

Kidneys and liver play an important role in maintenance of homeostasis.

27.5.5 Kidney failure, dialysis and kidney transplantCertain diseases or sometimes an accident may lead to kidney failure. Since the

number of nephrons is as large as almost one million in each kidney, a person can

survive even with one kidney. However, in case both the kidneys are damaged, it

is difficult to remain alive.

Modern technology can now save such patients with the helps of new

techniques like dialysis and kidney transplant. As shown in the figure (Fig. 27.10)

an artificial kidney is employed. A tube is inserted in an artery in the patients arm

or leg. The tube is connected to the kidney machine. This plastic tube has two

membranes so as to form one tube within the other. In the inner tube flows blood

from patients artery. This blood is surrounded by fluid (dialysis fluid) in theouter tube, separated from it by the membrane of the inner tube. Wastes move out

of blood into the fluid. The blood cleaned of its waste goes back from the kidney

machine into the vein in the arm or leg and back into the body. The kidney dialysis

fluid carrying waste is removed from the machine. This technique is termed

dialysis.

Nowadays, surgeon

sometimes remove a non-

functioning kidney from a patient

and replace it with a kidney

donated by another person. Care,however, has to be taken so that a

foreign kidney gets accepted by

the body.

CHECK YOUR PROGRESS

27.3

1. Define excretion.

2. Name the organ of the

excretory system, which

stores urine before its

removal from the body.

Line from artery

to apparatus

Fig. 27.10 Kidney dialysis

Pump

Tubing made of a

selectively permeable

membrane

Used dialyzing

solution (with urea

and excess salts)

Dialyzing

solutionLine from

apparatus to

vein

Fresh dialyzing

solution


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3. In which part of the nephron does filtration occur?

4. What happens to the useful substances that get filtered into the renal tubule?

5. What is osmoregulation?

TERMINAL EXERCISES

A. Multiple choice type questions.

Select the most appropriate answer of the following.

1. Which of the following is NOT a step in the process of respiration?

(a) Breathing

(b) Diffusion of oxygen from blood to tissues

(c) Diffusion of oxygen from tissues to blood

(d) Production of energy2. From which part of the respiratory system is oxygen picked up by the blood?

(a) Trachea (b) Bronchus (c) Alveolus (d) Nostrils

3. Which one of the following is not a part of nephron?

(a) Loop of Henle (b) Proximal Convoluted tubule (PCT)

(c) Distal Convoluted Tubule (DCT) (d) Seminiferous tubules.

4. Identify the process involved in the functioning of the artificial kidney.

(a) Renal transport (b) Dialysis (c) Renal failure (d) Catalysis

5. Which is the correct sequence of the following parts of the urinary system?

(A) Kidney (B) Ureter (C) Urethra (D) Urinary bladder

(a) B A C D ( b) D C B A (c) A B C D (d) A B D C

B. Fill in the blanks.

1. Excretion is a process of removal of _______________ waste.

2. Nephrons are the functional units of __________________

3. The main excretory nitrogenous product in human beings is _____________

4. The openings in plant leaves through which gaseous exchange takes place

arecalled _____________________

C. Descriptive type questions.

1. State one point of difference between each of the following:

(i) Breathing and respiration(ii) Inhalation and exhalation

(iii) Ureter and urethra

(iv) Homeostasis and osmoregulation

(v) Bowmans capsule and glomerulus

(vi) Bronchi and bronchioles

2. Which step occurs earlier than the other - breathing or cellular exchange of

gases?

3. What happens to the size of thoracic cavity when we breathe in air?

4. Describe the mechanism of breathing in human beings.


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5. How are respiratory gases exchanged between blood and tissues?

6. Draw the urinary system in the human body and label its parts.

7. What is glottis? Mention its function.8. Explain the mechanism of excretion.

9. Write notes on the following:

(i) artificial kidney (ii) glomerular filtrate

(iii) organs of excretion in human beings

ANSWERS TO CHECK YOUR PROGRESS

27.1

1. Air

2. Stomata

3. Through lenticels

4. Breathing is the mechanism for obtaining oxygen from the environment and

release carbon dioxide into it / respiration is the intake of oxygen as also its

utilization by cells for release of energy.

5. Energy is released through oxidation of food (glucose) during respiration in

cells.

27.2

1. The cartilaginous rings around the trachea prevent its collapse.

2. External nostrils, nasal cavity, internal nostrils, pharynx, trachea, bronchi,lungs.

3. The diaphragm contracts, thoracic cavity increases in volume, air from outside

rushes into lungs.

4. Mitochondria

5. They pick up oxygen from alveoli and carbon dioxide carried by them diffuses

into alveoli.

27.3

1. Excretion is the process of removal of nitrogenous waste products.

2. Urinary bladder3. Glomerulus

4. They are reabsorbed into blood

5. Maintaining the normal amount of water and mineral ions in blood is termed

Osmoregulation

GLOSSARY

Bowmans capsule: Thin walled cup-shaped part of the nephron with the

glomerulus lying within the cup. Bowmans capsule leads into the renal tubule.

Breathing: The mechanism in which oxygen from the environment is taken

into the lungs and carbon dioxide present in the lungs removed.


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Bronchitis: A respiratory disease in which the air passages in lungs become

inflamed.

Cellular respiration: The oxidation of glucose in the mitochondria of thecell.

Dialysis: The mechanism of cleansing the blood of its waste outside the body

by using a kidney machine.

Diaphragm: A muscular partition between the thoracic cavity and abdominal

cavity of mammals which participates in breathing.

Excretion: The process of elimination of nitrogenous waste products from

the body.

Exhalation: Removal of carbon dioxide from the lungs during breathing.

Glomerulus: A network of capillaries, which is a part of nephron.

Inhalation: Intake of oxygen-laden air into the lungs during breathing.

Lenticels: Tiny openings in older parts of roots and bark of woody plants for

exchange of gases.

Nephron: The structural and functional unit of the kidney. It is made of

glomerulus and renal tubule.

Pneumonia: The inflammation of lungs due to fluid accumulation in the

alveoli caused by bacterial infection.

Stomata: Openings in leaves which open and close for exchange of gases.

Respiration: The intake and utilization of oxygen for oxidation of glucose in

the cells for the liberation of energy.

Renal tubule: The tubular part of the nephron.

NIOS SSC SCIENCE LESSON Chapter 27

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